There are a great number of electroless copper deposition solutions currently employed. However, electroless copper deposits obtained from these solutions have some inherent stress (tensile or compressive). For printed circuit manufacture, an electroless copper deposit which is stress free is desirable. This is especially desirable for the so-called flexible printed circuits which require a certain degree of flexure.
Recently, methods have been reported in which electroless copper deposits can be applied to a broad variety of insulating substrate surfaces without the use of expensive noble metals but on the contrary, employ reducible salt compositions of non-noble metals. U.S. Pat. Nos. 3,772,056; 3,772,078; 3,907,621; 3,925,578; and 3,903,963 disclose such methods. A problem with the methods disclosed in these patents is that immersion in or treatment with a conventional electroless copper solution leads to at least partial destruction of a catalytic real image formed on the insulative surface unless the initiation time of the electroless copper deposition is rapid. It has been found that most electroless copper deposition baths or solutions do not have a rapid enough initiation rate.
An electroless copper deposition solution is currently commercially available and contains a source of cupric ions, i.e., cupric sulfate, a formaldehyde reducing agent, a phenyl mercuric acetate stabilizer, a mercuric acetate stabilizer, a potassium ferrocyanide accelerator and a complexing agent comprising N, N, N', N' tetrakis-(2-hydroxypropyl)-ethylenediamine ##STR1## The copper deposit obtained with such a solution has been found to contain stresses. The initiation rate of such a solution is rapid, but a more rapid initiation rate is desirable.